The present invention is directed in general to the field of electrophoretic analysis of liquid samples, such as biological specimens. More particularly, the invention is directed to a method and apparatus for automatically conducting electrophoresis with an electrophoresis plate.
Valuable information can be obtained by an analysis of certain biological fluids from a patient, such as blood serum, when diagnosing the patient's illness. Electrophoresis is known to be an effective technique for separating the various components of such fluid for subsequent analyses using optical densitometry techniques. The physical phenomenon underlying electrophoretic analysis is that particles which have an effective electric charge and which are deposited on a solid or semi-solid medium are caused to move with respect to the medium by an electric field applied across the medium. Particles of different types move at different rates, so a mixture of different types of particles is separated into its different components or fractions by electrophoretic analysis. These separated fractions may then be stained by exposing them to a suitable reagent so that the fractions can be optically detected using visible or ultraviolet light.
The electrophoresis process has been performed through a series of manual steps for many years. The manual process typically has started with the operator preparing an electrophoresis chamber by filling appropriate cavities of the chamber with buffer solution. Buffer solution is a liquid used in the electrophoresis process to maintain the surface of the electrophoretic medium in a moist condition and to provide an electrical interface to a power source applied to the chamber so that an electric field may be applied to the medium. The electrophoresis medium is typically a gel substance such as cellulose acetate or agarose that has been coated onto a Mylar (trademark) substrate to form an electrophoresis plate. The liquid sample to be examined is typically blood serum, but of course may be other liquids.
After the operator has prepared the electrophoresis chamber, he then applies consistent volumes of the samples to precise locations on the electrophoresis medium. The operator then places the medium into the electrophoresis chamber so that the edges of the medium are immersed in two buffer cavities at each of its longitudinal ends. Electrophoresis is then performed using a precise and consistent high voltage applied for a precise and consistent interval of time across the buffer cavities.
After electrophoresis has been completed, the operator applies a uniform coating of a staining reagent or stain to the surface of the medium, allowing a precise and consistent interval of time for the reagent and samples to chemically combine. The staining reagent is a liquid used after electrophoresis to chemically combine with the separated fractions of the fluid samples, causing the fractions to exhibit optical characteristics.
Next, the operator places the electrophoresis medium into a temperature-controlled oven and incubates it using a precise and consistent temperature and time interval. Incubation is the process of controlling the chemical reaction between the fractions of the liquid samples and the staining reagent by means of applying heat for a fixed interval of time.
Next, the operator dries the electrophoresis medium by increasing the oven temperature for a second precise and consistent temperature and time interval. The drying process stops the reaction between the separated fractions and the reagent by removing water from the medium. The medium can then be examined using optical densitometry techniques to determine which fractions were present in the original samples and to find their relative proportions.
The manual process described above requires careful attention by the operator in order to provide accurate and reproducible results. It is therefore not surprising that techniques for performing electrophoresis automatically have been developed. For example, U.S. Pat. Nos. 4,360,418 and 4,391,689 to Golias describe an automated electrophoresis and staining apparatus and method. U.S. Pat. Nos. 4,810,348, 4,890,247, 4,909,920, and 4,954,237 tc Sarrine et al also describe an automated electrophoresis apparatus and method. An automated applicator assembly with pipettes for transferring samples to the electrophoresis medium during automated analysis is described in U.S. Pat. Nos. 4,827,780 and 4,938,080 to Sarrine et al. All of these patents, which are assigned to the assignee of the present invention, are incorporated herein by reference.